if you are alternating between standard D and drop C, i'd recommend a .115 low string. maybe something like .95, .70, .50 for the rest? that should even out the tension some, and still give you a reasonably responsive low C.
for reference, my drop C set is .125, .90., .70, .50

- this would be too tight on the low string for standard D though.
and it does not account for the natural variable tension across the neck in 'normal' sets... i think i'll try a thicker .95 'A' (or G as it is) in future.